In manufacturing processes, e.g., of semiconductor equipment, when an interlayer dielectric (or insulation) film as an object to be processed (hereinafter also referred to as a “to-be-processed object”) is dry-etched in order to obtain a predetermined wiring pattern, a titanium nitride film is used as a hard mask which restricts the etching range. As this kind of hard mask, there is known one which is made up of a single layer of titanium nitride film (see, e.g., JP-A-2008-91915). The titanium nitride film for use as a hard mask requires etching resistance (etching durability) and, therefore, the film density shall preferably be high. On the other hand, if the film stress is high, at the time when the interlayer dielectric (insulation) film is subjected to dry etching, the etching shape changes as a whole or locally and, consequently, the wiring pattern will be deformed. Therefore, the film stress shall preferably be small to the extent possible.
It is normal practice to deposit the titanium nitride film that constitutes the above-described hard mask, by using a titanium-made target, considering the productivity and the like, by means of reactive sputtering in which nitrogen gas is introduced depending on necessity. In this case, when the sputtering conditions (electric power to be applied, amount of nitrogen gas to be introduced, speed of exhausting, and the like) are set so that the titanium nitride film has such a film density as will demonstrate (exert) etching resistance, the film stresses will become as high to the compressive side as about −1000 MPa. On the other hand, when the sputtering conditions (electric power to be applied, amount of nitrogen gas to be introduced, speed of exhausting, and the like) are set so that the film stress of the titanium nitride film becomes small so as to be above, e.g., −100 MPa and near 0 MPa, the film density enough to demonstrate etching resistance cannot be obtained. In other words, the titanium nitride film that has been deposited by reactive sputtering has a relationship in that, when the film stress of the titanium nitride film is reduced, the film density is also lowered substantially in proportion thereto. This is considered to be due to the physical properties of the titanium nitride film.
The inventor of this invention has proposed in Japanese Patent Application No. 2012-141440 that the hard mask be constituted by two layers of a lower-side titanium nitride layer (layer that lies on the lower side) which is relatively lower in film density and is also smaller in film stress, and an upper-side titanium nitride layer (layer that lies on the upper side) which is relatively higher in film density and is also larger in film stress. According to this arrangement, there can be obtained a titanium nitride film which has a film density enough to demonstrate etching resistance but which is smaller in film stress. However, there were problems, due to the two-layer structure, in that not only must the quality as the entire film be controlled, but also must the qualities of each of the films in the upper-side layer and the lower-side layer be controlled, thereby bringing about the troublesome control of qualities with resultant poor productivity.
The inventor then made further strenuous efforts and studies and has obtained the following finding. In other words, the finding is that, after having deposited a titanium nitride film of a single layer, oxygen-containing molecules are caused to get adsorbed onto the surface of the film, followed by raising in temperature of the titanium nitride film, the film stress can be made smaller to the tensile side while maintaining a high film density.